As is well known, most VCRs are provided with the capability of recording audio and video signals on audio and video tracks of a video tape, respectively, at one of several tape running speeds, e.g., standard playback (SP), long playback (LP), super long playback (SLP), according to a user's selection. In order to reproduce the audio and video signals recorded on the audio and video tracks at a same tape running speed as that chosen for their recording, mode information on the tape running speed is normally recorded together with other control information on a control track of the video tape.
In addition, in a recording system of a VCR, a color burst signal, which is known to be a reference signal to synchronize the phase of, e.g., 3.58 MHz color oscillator in a reproducing system of the VCR, is recorded on the video track of the video tape. Such a color burst signal, as is well known in the art, is inserted in a back porch of a horizontal synchronization signal in each horizontal blanking pulse of a composite video signal, as illustrated in FIG. 2. As shown in FIG. 2, the color burst signal is comprised of 8 to 12 cycles of, e.g., 3.58 MHz subcarrier, and the peak value thereof is one-half the horizontal synchronization signal. Peak-to-peak of the color burst signal equals the amplitude of the horizontal synchronization signal.
In case the composite video signal is recorded at one of the two tape running speeds of SP and SLP, the color burst signal is recorded after emphasizing the level thereof to, e.g., 6 dB, at an emphasizing device of the recording system. That is, at the emphasizing device, the amplitude of the color burst signal is amplified, e.g., two times, thereby emphasizing the level thereof to 6 dB. On the other hand, in case the composite video signal is recorded at the tape running speed of LP, the color burst signal is recorded after emphasizing the level thereof to 6 dB or without having no emphasis in response to an emphasis selection signal given in advance by the VCR manufacturing company. It is well known that a signal/noise (S/N) ratio of the color burst signal can increase by decreasing noises by recording the color burst signal after emphasizing it in the recording system.
In the reproducing system of the VCR, the composite video signal is read by a reproducing head of the VCR from the video track of the video tape and then is processed to reconstruct the original composite video signal. Specifically, in the reproducing system, an original chrominance signal of, e.g., 3.58 MHz is detected from the composite video signal by, e.g., band pass filters with cutoff frequencies of 629 KHz and 3.58 MHz; and then a color burst signal is extracted from the original chrominance signal by using a burst gate pulse generated by a burst gate pulse generator in the reproducing system.
Thereafter, the color burst signal is deemphasized by a deemphasizing device in the reproducing system to reconstruct an original color burst signal. In other words, in response to the mode information indicating the tape running speed of SP or SLP, read from the control track of the video tape, the color burst signal is deemphasized to a same level as that used to emphasize the color burst signal in the recording system. In response to the mode information representing the tape running speed of LP, however, the color burst signal is selectively deemphasized according to the emphasis selection signal predetermined at the emphasizing device of the recording system. That is, the color burst signal is deemphasized in response to the emphasis selection signal representing that it is preset to emphasize the color burst signal at the emphasizing device; and is not deemphasized in response to the emphasis selection signal indicating that it is preset not to emphasize the color burst signal at the emphasizing device. The non-deemphasized color burst signal or the deemphasized color burst signal is then provided to a next processor, e.g., a mixer, in the reproducing system to further process.
Since, however, the prior art reproducing system of the VCR performs the deemphasis for the color burst signal only in response to the emphasis selection signal preset at the VCR itself, without considering the amplitude of the color burst signal, the amount of the chrominance signal may decrease for instance when the color burst signal is a signal which has not been emphasized by another VCR. This results in a deterioration of the quality of the video signal reproduced by the reproducing system.